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[Bug gcov/profile/24487] [3.4/4.0/4.1 Regression] Basic block frequencies inaccurate
- From: "dje at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 28 Oct 2005 17:30:45 -0000
- Subject: [Bug gcov/profile/24487] [3.4/4.0/4.1 Regression] Basic block frequencies inaccurate
- References: <bug-24487-327@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #3 from dje at gcc dot gnu dot org 2005-10-28 17:30 -------
The misprediction causes (or at least contributes to) compute_alignments in
final.c not aligning the critical loop in longest_match. The recent changes to
bb-reorder.c moved the start of the loop from an ideal alignment to the worst
alignment, causing a 8-10% performance drop due to instruction fetch problems.
Without the explicit alignment directives omitted because of misprediction, the
alignment of the loop is random.
--
dje at gcc dot gnu dot org changed:
What |Removed |Added
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CC| |dberlin at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24487